[client] Add missing peer ACL flush (#3247)

Author: lixmal

client/firewall/nftables/acl_linux.go

@@ -348,6 +348,10 @@ func (m *AclManager) addIOFiltering(
 		UserData: userData,
 	})
 
+	if err := m.rConn.Flush(); err != nil {
+		return nil, fmt.Errorf(flushError, err)
+	}
+
 	rule := &Rule{
 		nftRule:    nftRule,
 		mangleRule: m.createPreroutingRule(expressions, userData),
@@ -359,6 +363,7 @@ func (m *AclManager) addIOFiltering(
 	if ipset != nil {
 		m.ipsetStore.AddReferenceToIpset(ipset.Name)
 	}
+
 	return rule, nil
 }